MINERAL PROCESSING KNOWLEDGE · DEWATERING
Thickening, filtration and dry tailings disposal form one continuous dewatering route, taking a 15-30% solids slurry to a conveyable cake and clear water that returns to the plant.
Technical overview. Actual process selection depends on representative ore samples, mineralogy, testwork and site conditions.
Both concentrates and tailings leave a mineral processing plant as dilute slurry, typically at 15% to 30% solids by weight. In that condition the material cannot be sold, cannot be trucked economically and cannot be stacked safely, so dewatering is not an administrative afterthought but a production stage in its own right. Industrial practice treats it as a three-stage route: thickening to remove the bulk of the water, filtration to reach a transportable cake, and dry tailings disposal to place the residue without a wet impoundment. Each stage has a defined duty, and each depends on the stage before it working properly.
Technical note: The figures below are typical operating ranges. Actual performance depends on particle size distribution, clay and slime content, surface chemistry, flocculant selection and the site water balance, and should be confirmed by testwork on representative slurry.
1. Thickening: taking out the bulk of the water
The first stage is a high-rate thickener. Its job is volume reduction rather than drying: the feed slurry at 15% to 30% solids is concentrated to 50% to 70% solids in the underflow, while a clear overflow leaves at the top and is returned directly to the plant as process water. A well-run thickener therefore removes most of the water and most of the footprint problem at the same time.
The mechanism is assisted settling. A high molecular weight flocculant, typically a polyacrylamide, is dosed into the feed to bridge fine particles into large flocs. Those flocs settle far faster than individual particles would, which is what makes a high-rate unit compact and what allows the overflow to be clean enough for reuse. Without flocculation, fine slimes settle slowly, the overflow carries solids and the entire downstream water balance deteriorates.
- Feed condition: 15% to 30% solids by weight, which is why thickening is needed before any handling or transport decision.
- Target underflow: 50% to 70% solids, a pumpable but much denser pulp for filtration.
- Flocculant duty: to bind fine particles into large flocs and accelerate settling.
- Overflow duty: clear water returned to the process, which is where most of the water saving is realised.
- Operating checkpoints: feed density, flocculant make-up and dosing, bed level, rake load and overflow clarity.
2. Filtration: from pulp to conveyable cake
The second stage forces the remaining water out of the thickened pulp under pressure or vacuum. Recessed plate filter presses and ceramic disc filters are both used for this duty, the first applying high-pressure pumping and the second vacuum to draw water through a filter medium. The product is a solid cake with moisture reduced to 8% to 15%, which is the range in which material can be carried on a belt conveyor and loaded into trucks without free water.
Filtration is the stage where the previous one shows up. A feed that is too dilute extends cycle times and produces a wetter cake; a feed with high slime or clay content blinds the medium and lowers throughput. Cake moisture at 8% to 15% is not simply a quality figure: it determines whether the material can be transported, what the transport cost per tonne will be, and whether the tailings can be stacked in lifts rather than pumped as slurry.
| Stage | Typical equipment | Mechanism | Result |
|---|---|---|---|
| 1. Thickening | High-rate thickener | Flocculant-assisted settling of fine particles into large flocs | Slurry raised from 15-30% to 50-70% solids; clear overflow returned to the plant |
| 2. Filtration | Recessed plate filter press or ceramic disc filter | High-pressure pumping or vacuum drawing water through a filter medium | Solid filter cake with moisture of 8-15%, suitable for belt conveying and truck loading |
| 3. Dry tailings disposal | Belt conveyor and dry stacking facility | Layered compaction of the filtered residue | Wet tailings impoundment eliminated; process water recovery above 95% |
3. Dry tailings disposal and the water balance
The third stage is a planning and materials handling decision as much as an equipment one. Filtered dry residue is carried by belt conveyor to a dry tailings storage facility and compacted in layers. Because the material arrives as a moist solid rather than as a slurry, the conventional high-risk wet tailings pond is no longer required for that stream, and with it goes the associated dam safety exposure.
The environmental and operating case follows from the water balance. When the thickener overflow is returned, the filtrate is recovered and the cake is stacked rather than impounded, so process water recycling can exceed 95%. That reduction in make-up water demand is often the difference between a viable site and one that cannot be permitted, and it aligns the operation with green mine construction requirements. The same logic applies to concentrate dewatering.
The sequence only works as a chain: a thickener that underperforms overloads the filter press, a wet cake makes dry stacking impossible and pushes the operation back to slurry disposal, and a disposal plan that cannot accept the cake limits how hard the first two stages can be pushed. Design the three together and size each one on testwork.
Conclusion
Dewatering is a three-stage route with a clear division of labour. Thickening uses flocculation to lift a 15% to 30% slurry to 50% to 70% solids and returns clear water to the plant. Filtration presses the pulp into a cake of 8% to 15% moisture that can be conveyed and trucked. Dry tailings disposal stacks that cake in layers and removes the wet impoundment, and with water recovery above 95% the route becomes a water management strategy as much as a solids handling one.
How LiCheng Tech can help
LiCheng Tech supplies thickening, filtration, tailings handling and water recovery equipment for mineral processing plants, and integrates them with the upstream washing and classification circuit so that the solids balance and the water balance are designed together. Send us your slurry density, particle size distribution, slime content and site water constraints, and our engineers will help define the three-stage route, select equipment for each duty and identify the points where testwork will change the design. Review the filter press, concentrator and fine sand recovery pages for the equipment used at each stage.
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